I think first we should arrange a Skype call with pang here, maybe mum too than all this can come out easy and we can then translate and clears the air one way or another
That done i now feel you give thought to coming later rather than around Christmas for the following
1 First your dad
2 Flights are most expensive until after Jan 15th - then 20% lower
3 New year to a Thai is same as our Christmas. Party party party, everything stops for 1 week. Pang will want to be with family as they all do, - you could be the ATM for that !!!!
4 sort the relationship out in detail, be sure, very sure as taking her to the US is expensive. As said to you before getting this right is better than quick
5 Getting around, travel is difficult and dangerous New year - lots of road accidents - drink related
6 Getting married January better than before New year all round